Various embodiments described herein relate generally to methods for cleaning a glass substrate and related cleaning solutions. These methods and related cleaning solutions can be particularly effective for removing metal ion contaminates from a glass substrate having a transparent conductive oxide layer (“TCO glass”). Such glass substrates are used in the formation of some thin-film single-junction and multi-junction solar cells.
Current methods for forming thin-film solar cells involve depositing or otherwise forming a plurality of layers on a substrate, such as a glass, metal or polymer substrate suitable to form one or more p-n junctions. An exemplary thin solar cell includes a glass substrate having a TCO layer, a plurality of doped and undoped silicon layers, and a metal back layer.
TCO glass can be manufactured on or off a production line. On-line production of TCO glass is relatively inexpensive. However, because a glass production line is relatively dirty, on-line production of TCO glass typically results in the presence of significant amounts of metal ion contaminants on the TCO layer, such as Fe, Cu, Mg, Ca, Na, K, and the like. In contrast, off-line production of TCO glass results in relatively low levels of metal ion contaminates on the TCO layer, but is relatively expensive.
While it is preferable to employ less expensive components so as to reduce the cost of resulting solar panels, there is a concern that TCO layer metal ion contamination may degrade a solar panel's efficiency over time. The concern relates to the possibility that the metal ion contaminates on the TCO layer may diffuse into the adjacent silicon layers and thereby degrade the performance of the solar cell.
Accordingly, it is desirable to develop methods and related cleaning solutions that can remove metal ion contaminates from a glass substrate. More particularly, it is desirable to develop methods and related cleaning solutions that can remove metal ion contaminates from TCO glass used in the manufacture of thin-film solar cells.